Manually operated air pumps are known in the art. By "pump" is meant a device which causes fluid flow and which preferably compresses a gaseous fluid and delivers it under pressure to an enclosed vessel or space. By "air" is meant any gas and most preferably ambient air. Hand pumps frequently require the user to press against a handle or similar device to compress trapped air via a cylinder and force it to pass through a hose which is attached to the device for which compressed air is required. A one-way valve is often employed at the device to prevent exit of the compressed air. Hand operated pumps are generally one stage pumps and air is typically drawn into the pump when the user pulls up on the handle. One stage hand operated pumps are not particularly difficult to use when the device to be filled is empty and the user is pushing against ambient or air pressure. A continuing drawback of hand operated pumps becomes immediately apparent when the user attempts to press against a high back pressure which is present, for example, near the end of a filling operation or to "top-off" an already inflated device. The higher the existing back pressure cf the compressed air already within the device to be filled, the greater the physical force required by the user to drive the pump and complete the task.
Serious cyclists use light-weight, tubular thin-walled tires for racing or extended touring. Because the tubular tires are vulnerable to punctures and other road damages, cyclists may carry spare tires which may be mounted and used until the damaged tire can be repaired. A tubular tire may be inflated at pressures frequently above 120 pounds per square inch and ranging from 45 pounds per square inch to 135 pounds per square inch, depending upon the riding conditions. In addition, it may be necessary to vary the pressure during a particular excursion.
Hand-operated air pumps are frequently carried by cyclists for the inflation of bicycle tires. The pumps must be compact, portable and light weight. Conventional reciprocating pumps have been adapted for use by cyclists. The reciprocating pumps operate with a small volume cylinder and a small diameter piston displacing very limited air volumes and requiring considerable time to inflate the tire. Those small displacement compressors result in a considerable amount of muscular energy being expended. The most compact of these prior pumps uses rather uncomfortable muscular exertion, particularly pushing motions, to achieve compression of the air. It is difficult to achieve pressures at the upper end of the inflation pressure scale with known hand operated pumps.
As can be seen from the discussion of the prior art, an unsolved need exists for a manually operated pump having simple mechanical structures for rapidly and easily converting relatively non-strenuous muscular effort to useful high pressure compressed air.